+, -, *, /, ^ , Div, Mod , Gcd , Lcm , <<, >> , FromBase, ToBase , Precision , GetPrecision , N , Rationalize , IsPrime , IsPrimePower , Factors , Factor , PAdicExpand , ContFrac , ContFracList, ContFracEval , GuessRational, NearRational , Decimal , TruncRadian , Floor , Ceil , Round , Pslq .

# Arithmetic and other operations on numbers

Besides the usual arithmetical operations, Yacas defines some more advanced operations on numbers. Many of them also work on polynomials.

+, -, *, /, ^ | Arithmetic operations
Div, Mod | Division with remainder
Gcd | Greatest common divisor
Lcm | Least common multiple
<<, >> | Shift operators
FromBase, ToBase | Conversion from/to non-decimal base
Precision | Sets the precision
GetPrecision | Returns the current precision
N | Numerical approximation
Rationalize | Convert floating point numbers to fractions
IsPrime | Test for a prime number
IsPrimePower | Test for a power of a prime number
Factors | Factorization
Factor | Factorization, in pretty form
PAdicExpand | p-adic expansion
ContFrac | continued fraction expansion
ContFracList, ContFracEval | manipulate continued fractions
GuessRational, NearRational | find optimal rational approximations
Decimal | decimal representation of a rational
TruncRadian | remainder modulo 2*Pi
Floor | Round a number downwards
Ceil | Round a number upwards
Round | Round a number to the nearest integer
Pslq | Search for integer relations between reals

###

+, -, *, /, ^ -- Arithmetic operations

Standard math library

##### Calling format:

    x+y  (precedence 6)
    +x
    x-y  (precedence 5)
    -x
    x*y  (precedence 3)
    x/y  (precedence 3)
    x^y  (precedence 2)

##### Parameters:

`x` and `y` - objects for which arithmetic operations are defined

##### Description:

These are the basic arithmetic operations. They can work on integers, rational numbers, complex numbers, vectors, matrices and lists.

These operators are implemented in the standard math library (as opposed to being built-in). This means that they can be extended by the user.

##### Examples:

    In> 2+3
    Out> 5;
    In> 2*3
    Out> 6;

###

Div, Mod -- Division with remainder

Standard math library

##### Calling format:

    Div(x,y)
    Mod(x,y)

##### Parameters:

`x`, `y` - integers or univariate polynomials

##### Description:

`Div` performs integer division and `Mod` returns the remainder after division. `Div` and `Mod` are also defined for polynomials.

If `Div(x,y)` returns "a" and `Mod(x,y)` equals "b", then these numbers satisfy x=a*y+b and 0<=b<y.

##### Examples:

    In> Div(5,3)
    Out> 1;
    In> Mod(5,3)
    Out> 2;

##### See also:

Gcd , Lcm .

###

Gcd -- Greatest common divisor

Standard math library

##### Calling format:

    Gcd(n,m)
    Gcd(list)

##### Parameters:

`n`, `m` - integers or univariate polynomials

`list` - a list of all integers or all univariate polynomials

##### Description:

This function returns the greatest common divisor of "n" and "m". The gcd is the largest number that divides "n" and "m". It is also known as the highest common factor (hcf). The library code calls `MathGcd`, which is an internal function. This function implements the "binary Euclidean algorithm" for determining the greatest common divisor:

##### Routine for calculating `Gcd(n,m)`

- if n=m then return n
- if both n and m are even then return 2*Gcd(n/2,m/2)
- if exactly one of n or m (say n) is even then return Gcd(n/2,m)
- if both n and m are odd and, say, n>m then return Gcd((n-m)/2,m)

This is a rather fast algorithm on computers that can efficiently shift integers.

If the second calling form is used, `Gcd` will return the greatest common divisor of all the integers or polynomials in "list". It uses the identity

Gcd(a,b,c)=Gcd(Gcd(a,b),c)

##### Examples:

    In> Gcd(55,10)
    Out> 5;
    In> Gcd({60,24,120})
    Out> 12;

##### See also:

Lcm .

###

Lcm -- Least common multiple

Standard math library

##### Calling format:

    Lcm(n,m)

##### Parameters:

`n`, `m` -- integers or univariate polynomials

##### Description:

This command returns the least common multiple of "n" and "m". The least common multiple of two numbers "n" and "m" is the lowest number which is an integer multiple of both "n" and "m". It is calculated with the formula:

    $$Lcm(n,m) = Div(n*m,Gcd(n,m))$$

This means it also works on polynomials, since `Div`, `Gcd` and multiplication are also defined for them.

##### Examples:

    In> Lcm(60,24)
    Out> 120;

##### See also:

Gcd .

###

<<, >> -- Shift operators

Standard math library

##### Calling format:

    n<>m

##### Parameters:

n, m - integers

##### Description:

These operators shift integers to the left or to the right. They are similar to the C shift operators. These are sign-extended shifts, so they act like multiplication or division by powers of 2.

##### Examples:

    In> 1 << 10
    Out> 1024;
    In> -1024 >> 10
    Out> -1;

###

FromBase, ToBase -- Conversion from/to non-decimal base

Internal function

##### Calling format:

    FromBase(base,number)
    ToBase(base,number)

##### Parameters:

base - a base to write the numbers in

number - a number to write out in the base representation

##### Description:

`FromBase` converts "number", written in base "base", to base 10. `ToBase` converts "number", written in base 10, to base "base".

These functions use the p-adic expansion capabilities of the built-in arbitrary precision math libraries.

##### Examples:

    In> FromBase(2,111111)
    Out> 63;
    In> ToBase(16,255)
    Out> ff;

The first command writes the binary number `111111` in decimal base. The second command converts `255` (in decimal base) to hexadecimal base.

##### See also:

PAdicExpand .

###

Precision -- Sets the precision

Internal function

##### Calling format:

    Precision(n)

##### Parameters:

n - new precision

##### Description:

This command sets the number of binary digits to be used in calculations. All subsequent floating point operations will allow for at least "n" digits after the decimal point.

##### Examples:

    In> Precision(10)
    Out> True;
    In> N(Sin(1))
    Out> 0.8414709848;
    In> Precision(20)
    Out> True;
    In> N(Sin(1))
    Out> 0.84147098480789650665;
    In> GetPrecision()
    Out> 20;

##### See also:

GetPrecision , N .

###

GetPrecision -- Returns the current precision

Internal function

##### Calling format:

    GetPrecision()

##### Description:

This command returns the current precision, as set by `Precision`.

##### Examples:

    In> GetPrecision();
    Out> 10;
    In> Precision(20);
    Out> True;
    In> GetPrecision();
    Out> 20;

##### See also:

Precision , N .

###

N -- Numerical approximation

Standard math library

##### Calling format:

N(expr)

N(expr, prec)

##### Parameters:

expr - expression to evaluate

prec - precision to use

##### Description:

This function forces Yacas to give a numerical approximation to the expression "expr", using "prec" digits if the second calling sequence is used, and the precision as set by `SetPrecision` otherwise. This overrides the normal behaviour, in which expressions are kept in symbolic form (eg. `Sqrt(2)` instead of `1.41421`).

Application of the `N` operator will make Yacas calculate floating point representations of functions whenever possible. In addition, the variable `Pi` is bound to the value of Pi up to the required precision.

##### Examples:

    In> 1/2
    Out> 1/2;
    In> N(1/2)
    Out> 0.5;
    In> Sin(1)
    Out> Sin(1);
    In> N(Sin(1),10)
    Out> 0.8414709848;
    In> Pi
    Out> Pi;
    In> N(Pi,20)
    Out> 3.14159265358979323846;

##### See also:

Precision , GetPrecision , Pi .

###

Rationalize -- Convert floating point numbers to fractions

Standard math library

##### Calling format:

    Rationalize(expr)

##### Parameters:

expr - an expression containing real numbers

##### Description:

This command converts every real number in the expression "expr" into a rational number. This is useful when a calculation needs to be done on floating point numbers and the algorithm is unstable. Converting the floating point numbers to rational numbers will force calculations to be done with infinite precision (by using rational numbers as representations).

It does this by finding the smallest integer n such that multiplying the number with 10^n is an integer. Then it divides by 10^n again, depending on the internal gcd calculation to reduce the resulting division of integers.

##### Examples:

    In> {1.2,3.123,4.5}
    Out> {1.2,3.123,4.5};
    In> Rationalize(%)
    Out> {6/5,3123/1000,9/2};

##### See also:

IsRational .

###

IsPrime -- Test for a prime number

Standard math library

##### Calling format:

    IsPrime(n)

##### Parameters:

n - integer to test

##### Description:

This command checks whether "n", which should be a positive integer, is a prime number. A number is a prime number if it is only divisible by 1 and itself. As a special case, 1 is not a prime number.

This function essentially checks for all integers between 2 and the square root of "n" whether they divide "n", and hence may take a long time for large numbers.

##### Examples:

    In> IsPrime(1)
    Out> False;
    In> IsPrime(2)
    Out> True;
    In> IsPrime(10)
    Out> False;
    In> IsPrime(23)
    Out> True;
    In> Select("IsPrime", 1 .. 100)
    Out> {2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,
      53,59,61,67,71,73,79,83,89,97};

##### See also:

IsPrimePower , Factors .

###

IsPrimePower -- Test for a power of a prime number

Standard math library

##### Calling format:

    IsPrimePower(n)

##### Parameters:

n - integer to test

##### Description:

This command tests whether "n", which should be a positive integer, is a prime power, that is whether it is of the form p^m, with "p" prime and "m" an integer.

This function essentially checks for all integers between 2 and the square root of "n" for the largest divisor, and then tests whether "n" is a power of this divisor. So it will take a long time for large numbers.

##### Examples:

    In> IsPrimePower(9)
    Out> True;
    In> IsPrimePower(10)
    Out> False;
    In> Select("IsPrimePower", 1 .. 50)
    Out> {2,3,4,5,7,8,9,11,13,16,17,19,23,25,27,
      29,31,32,37,41,43,47,49};

##### See also:

IsPrime , Factors .

###

Factors -- Factorization

Standard math library

##### Calling format:

    Factors(x)

##### Parameters:

x - integer or univariate polynomial

##### Description:

This function decomposes the integer number "x" into a product of numbers. Alternatively, if "x" is a univariate polynomial, it is decomposed in irreducible polynomials.

The factorization is returned as a list of pairs. The first member of each pair is the factor, while the second member denotes the power to which this factor should be raised. So the factorization x=p1^n1*...*p9^n9 is returned as `{{p1,n1}, ..., {p9,n9}}`.

##### Examples:

    In> Factors(24);
    Out> {{2,3},{3,1}};
    In> Factors(2*x^3 + 3*x^2 - 1);
    Out> {{2,1},{x+1,2},{x-1/2,1}};

##### See also:

Factor , IsPrime .

###

Factor -- Factorization, in pretty form

Standard math library

##### Calling format:

    Factors(x)

##### Parameters:

x - integer or univariate polynomial

##### Description:

This function factorizes "x", like `Factors`, but it shows the result in a nicer human readable format.

##### Examples:

    In> PrettyForm(Factor(24));

     3
    2  * 3

    Out> True;
    In> PrettyForm(Factor(2*x^3 + 3*x^2 - 1));

                 2   /     1 \
    2 * ( x + 1 )  * | x - - |
                     \     2 /

    Out> True;

##### See also:

Factors , IsPrime , PrettyForm .

###

PAdicExpand -- p-adic expansion

Standard math library

##### Calling format:

    PAdicExpand(n, p)

##### Parameters:

`n` - number, or polynomial, to expand

`p` - base to expand in

##### Description:

This command computes the p-adic expansion of "n". In other words, "n" is expanded in powers of "p". The argument "n" can be either an integer or a univariate polynomial. The base "p" should be of the same type.

##### Examples:

    In> PrettyForm(PAdicExpand(1234, 10));

                   2     3
    3 * 10 + 2 * 10  + 10  + 4

    Out> True;
    In> PrettyForm(PAdicExpand(x^3, x-1));

                                 2            3
    3 * ( x - 1 ) + 3 * ( x - 1 )  + ( x - 1 )  + 1

    Out> True;

##### See also:

Mod , ContFrac , FromBase , ToBase .

###

ContFrac -- continued fraction expansion

Standard math library

##### Calling format:

    ContFrac(x)
    ContFrac(x, depth)

##### Parameters:

`x` - expression to expand in continued fractions

`depth` - maximum required depth of result

##### Description:

This command returns the continued fraction expansion of `x`, which should be either a floating point number or a polynomial. If `depth` is not specified, it defaults to 6. The remainder is denoted by `rest`.

This is especially useful for polynomials, since series expansions that converge slowly will typically converge a lot faster if calculated using a continued fraction expansion.

##### Examples:

    In> PrettyForm(ContFrac(N(Pi)))

                 1
    --------------------------- + 3
               1
    ----------------------- + 7
            1
    ------------------ + 15
          1
    -------------- + 1
       1
    -------- + 292
    rest + 1

    Out> True;
    In> PrettyForm(ContFrac(x^2+x+1, 3))

           x
    ---------------- + 1
             x
    1 - ------------
           x
        -------- + 1
        rest + 1

    Out> True;

##### See also:

ContFracList , NearRational , GuessRational , PAdicExpand , N .

###

ContFracList, ContFracEval -- manipulate continued fractions

Standard math library

##### Calling format:

    ContFracList(frac)
    ContFracList(frac, depth)
    ContFracEval(list)
    ContFracEval(list, rest)

##### Parameters:

`frac` -- a number to be expanded

`depth` -- desired number of terms

`list` -- a list of coefficients

`rest` -- expression to put at the end of the continued fraction

##### Description:

The function `ContFracList` computes terms of the continued fraction representation of a rational number `frac`. It returns a list of terms of length `depth`. If `depth` is not specified, it returns all terms.

The function `ContFracEval` converts a list of coefficients into a continued fraction expression. The optional parameter `rest` specifies the symbol to put at the end of the expansion. If it is not given, the result is the same as if `rest=0`.

##### Examples:

    In> A:=ContFracList(33/7 + 0.000001)
    Out> {4,1,2,1,1,20409,2,1,13,2,1,4,1,1,3,3,2};
    In> ContFracEval(Take(A, 5))
    Out> 33/7;
    In> ContFracEval(Take(A,3), remainder)
    Out> 1/(1/(remainder+2)+1)+4;

##### See also:

ContFrac , GuessRational .

###

GuessRational, NearRational -- find optimal rational approximations

Standard math library

##### Calling format:

    GuessRational(x)
    GuessRational(x, digits)
    NearRational(x)
    NearRational(x, digits)

##### Parameters:

`x` -- a number to be approximated

`digits` -- desired number of decimal digits

##### Description:

The functions `GuessRational(x)` and `NearRational(x)` attempt to find "optimal" rational approximations to a given value `x`. The approximations are "optimal" in the sense of having smallest numerators and denominators among all rational numbers close to `x`. This is done by computing a continued fraction representation of `x` and truncating it at a suitably chosen term. Both functions return a rational number which is an approximation of `x`.

Unlike the function `Rationalize()` which converts floating-point numbers to rationals without loss of precision, the functions `GuessRational()` and `NearRational()` are intended to find the best rational that is approximately equal to a given value.

The function `GuessRational()` is useful if you have obtained a floating-point representation of a rational number and you know approximately how many digits its exact representation should contain. This function takes an optional second parameter `digits` which limits the number of decimal digits in the denominator of the resulting rational number. If this parameter is not given, it defaults to half the current precision. This function truncates the continuous fraction expansion when it encounters an unusually large value (see example). This procedure does not always give the "correct" rational number; a rule of thumb is that the floating-point number should have at least as many digits as the combined number of digits in the numerator and the denominator of the correct rational number.

The function `NearRational(x)` is useful if you would like to simply approximate a given value, i.e. to find an "optimal" rational number that lies in a certain small interval around a certain value `x`. This function takes an optional second parameter `digits` which has slightly different meaning: it specifies the number of digits of precision of the approximation; in other words, the difference between `x` and the resulting rational number should be at most one digit of that precision. The parameter `digits` also defaults to half of the current precision.

##### Examples:

Start with a rational number and obtain a floating-point approximation:

    In> x:=N(956/1013)
    Out> 0.9437314906
    In> Rationalize(x)
    Out> 4718657453/5000000000;
    In> V(GuessRational(x))
    GuessRational: using 10 terms of the
      continued fraction
    Out> 956/1013;
    In> ContFracList(x)
    Out> {0,1,16,1,3,2,1,1,1,1,508848,3,1,2,1,2,2};

The first 10 terms of this continued fraction correspond to the correct continued fraction for the original rational number.

    In> NearRational(x)
    Out> 218/231;

This function found a different rational number closeby because the precision was not high enough.

    In> NearRational(x, 10)
    Out> 956/1013;

##### See also:

ContFrac , ContFracList , Rationalize .

###

Decimal -- decimal representation of a rational

Standard math library

##### Calling format:

    Decimal(frac)

##### Parameters:

`frac` - a rational number

##### Description:

This function returns the infinite decimal representation of a rational number `frac`. It returns a list, with the first element being the number before the decimal point and the last element the sequence of digits that will repeat forever. All the intermediate list elements are the initial digits before the period sets in.

##### Examples:

    In> Decimal(1/22)
    Out> {0,0,{4,5}};
    In> N(1/22,30)
    Out> 0.045454545454545454545454545454;

##### See also:

N .

###

TruncRadian -- remainder modulo 2*Pi

Standard math library

##### Calling format:

    TruncRadian(r)

##### Parameters:

`r` - a number

##### Description:

`TruncRadian` calculates Mod(r,2*Pi), returning a value between 0 and 2*Pi. This function is used in the trigonometry functions, just before doing a numerical calculation using a Taylor series. It greatly speeds up the calculation if the value passed is a large number.

The library uses the formula

TruncRadian(r)=r-Floor(r/(2*Pi))*2*Pi
where r and 2*Pi are calculated with twice the precision used in the environment to make sure there is no rounding error in the significant digits.

##### Examples:

    In> 2*Pi()
    Out> 6.283185307;
    In> TruncRadian(6.28)
    Out> 6.28;
    In> TruncRadian(6.29)
    Out> 0.0068146929;

##### See also:

Sin , Cos , Tan .

###

Floor -- Round a number downwards

Standard math library

##### Calling format:

    Floor(x)

##### Parameters:

x - a number

##### Description:

This function returns the largest integer smaller than "x".

##### Examples:

    In> Floor(1.1)
    Out> 1;
    In> Floor(-1.1)
    Out> -2;

##### See also:

Ceil , Round .

###

Ceil -- Round a number upwards

Standard math library

##### Calling format:

    Ceil(x)

##### Parameters:

x - a number

##### Description:

This function returns the smallest integer larger than "x".

##### Examples:

    In> Ceil(1.1)
    Out> 2;
    In> Ceil(-1.1)
    Out> -1;

##### See also:

Floor , Round .

###

Round -- Round a number to the nearest integer

Standard math library

##### Calling format:

    Round(x)

##### Parameters:

x - a number

##### Description:

This function returns the integer closest to "x". Half-integers (i.e. numbers of the form n+0.5, with n an integer) are rounded upwards.

##### Examples:

    In> Round(1.49)
    Out> 1;
    In> Round(1.51)
    Out> 2;
    In> Round(-1.49)
    Out> -1;
    In> Round(-1.51)
    Out> -2;

##### See also:

Floor , Ceil .

###

Pslq -- Search for integer relations between reals

Standard math library

##### Calling format:

    Pslq(xlist,precision)

##### Parameters:

`xlist` - list of numbers

precision - required number of digits precision of calculation

##### Description:

This function is an integer relation detection algorithm. This means that, given the numbers x[i] in the list "xlist", it tries to find integer coefficients a[i] such that a[1]*x[1] + ... + a[n]*x[n]=0. The list of integer coefficients is returned.

The numbers in "xlist" must evaluate to floating point numbers if the `N` operator is applied on them.

##### Example:

    In> Pslq({ 2*Pi+3*Exp(1) , Pi , Exp(1) },20)
    Out> {1,-2,-3};

Note: in this example the system detects correctly that 1*(2*Pi+3*e)+(-2)*Pi+(-3)*e=0.

##### See also:

N .